Scanning electron microscopes (SEM) or transmission electron microscopes (TEM) are used to observe infinitesimal regions of an object. Generally, these devices evacuate an enclosure that houses a sample to get images of the sample in a vacuum state. However, biochemical samples or liquid samples can be damaged in vacuum or can be changed in nature therein. Meanwhile, there has been a strong need for observing such samples under electron microscope. In recent years, there have been developed SEM equipment and sample holding devices that allow an observation target sample to be observed at atmospheric pressure.
In principle, these devices set up a permeable diaphragm or a tiny through hole that allows an electron beam to pass therethrough between an electron optical system and the sample, thereby separating the vacuum state from the atmospheric state. Common to these devices is the provision of the diaphragm between the sample and the electron optical system.
For example, Patent Document 1 discloses an SEM in which an electron optical tube has its electron source oriented downward and its objective lens oriented upward. The end of the electron optical tube emitting an electron beam has a diaphragm with an O-ring allowing the electron beam to pass through an emitting hole of the tube. According to the invention described in this literature, the observation target sample is directly placed on the diaphragm. The sample is then irradiated from below with a primary electron beam so that reflected or secondary electrons are detected for SEM observation. The sample is held in a space made up of the diaphragm and a circular member surrounding the diaphragm. Furthermore, this space is filled with liquid such as water.